一、环境说明：

本博文的演示环境和上篇博文一致
https://blog.51cto.com/wujianwei/2374588

1.1简述：

基于上篇博文，为了部署mysqlpxc集群环境，需要开启3个vmware虚拟机实例来部署3个mysqlpxc实例。
第一篇博文中在初始化mysqlpxc实例后，登录实例时，报错提示：

[root@pxc01 local]# /usr/local/mysqlpxc/bin/mysql -uroot -p
mysql: error while loading shared libraries: libreadline.so.6: cannot open shared object file: No such file or directory
[root@pxc01 local]# ldd /usr/local/mysqlpxc/bin/mysql
ldd: ./mysql: not regular file
[root@pxc01 local]# ldd /usr/bin/mysql
linux-vdso.so.1 =>  (0x00007ffd38da9000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f91bc012000)
libreadline.so.6 => not found

找不到库文件 libreadline.so.6，出现这样的问题主要是当时自己在上篇博文的环境中卸载了 readline-6.2-10.el7.x86_64 这个文件导致的找不到 libreadline.so.6 库文件

[root@pxc01 ~]# rpm -qa|grep readline-6.2-10.el7.x86_64
readline-6.2-10.el7.x86_64
[root@pxc01 ~]# rpm -e --nodeps readline-6.2-10.el7.x86_64

于是重新安装 yum install -y readline-devel readline

[root@pxc01 local]# rpm -qa|grep readline*
readline-devel-6.2-10.el7.x86_64
readline-6.2-10.el7.x86_64

到此处第一篇博文找不到libreadline.so.6库文件的问题才得以解决。

二、解决libreadline.so.7找不到的问题

接下来才是本博文要重点阐述的问题。
当然此问题的引出还是和上一篇的博文分不开的。

2.1环境简单说明:

vmware 虚拟机，系统centos7.2,mysqlpxc 版本5.7.24，二进制版本安装。firewalld 和iptables关闭，selinux关闭。单台虚拟机安装单实例mysqlpxc服务。初始化mysqlpxc 和启动mysqlpxc都是参照上一篇博文https://blog.51cto.com/wujianwei/2374588成功部署。
但是在登录mysqlpxc实例时，依旧报错如下：

[root@pxc02 data]# /usr/local/mysqlpxc/bin/mysql -uroot -p
/usr/local/mysqlpxc/bin/mysql: error while loading shared libraries: libreadline.so.7: cannot open shared object file: No such file or directory
[root@pxc02 mysql3308]# ldd /usr/local/mysqlpxc/bin/mysql|grep 'not found'
libreadline.so.7 => not found
[root@pxc02 mysql3308]# find / -name 'libreadline.so.7'
[root@pxc02 mysql3308]#
[root@pxc02 mysql3308]# rpm -qa|grep readline*
readline-6.2-9.el7.x86_64

于是换了一种思路来解决此问题。不再采用上篇博文的方式。

2.2 解决过程：

首先尝试 yum install -y readline-devel readline,本以为可以解决然而并无卵用，依然报错

[root@pxc02 mysql3308]# yum install -y readline-devel readline
[root@pxc02 mysql3308]# rpm -qa|grep readline*
readline-devel-6.2-10.el7.x86_64
readline-6.2-10.el7.x86_64
[root@pxc02 mysql3308]#  /usr/local/mysqlpxc/bin/mysql -uroot -p',pL*O3dLkWk)'
/usr/local/mysqlpxc/bin/mysql: error while loading shared libraries: libreadline.so.7: cannot open shared object file: No such file or directory

[root@pxc02 mysql3308]# ldd /usr/local/mysqlpxc/bin/mysql|grep 'not found'
libreadline.so.7 => not found

于是换了一种思路，尝试×××器上存在的libreadline.so 库文件有哪些？

[root@pxc02 mysql3308]# find / -name 'libreadline.so*'
/usr/lib64/libreadline.so.6.2
/usr/lib64/libreadline.so
/usr/lib64/libreadline.so.6

[root@pxc02 mysql3308]# ll /usr/lib64/libreadline.so.6
lrwxrwxrwx 1 root root 18 Feb 24 09:33 /usr/lib64/libreadline.so.6 -> libreadline.so.6.2
[root@pxc02 mysql3308]# ll /usr/lib64/libreadline.so.6.2
-rwxr-xr-x 1 root root 285240 Aug  2  2017 /usr/lib64/libreadline.so.6.2

发现源文件是libreadline.so.6.2 ，而libreadline.so.6 这个文件为源文件libreadline.so.6.2创建的软连接。

根据下面的库文件的指向，断定后面的文件应该都是源库文件的软连接，而libreadline.so.7 => not found 提示找不到软连接文件的位置，于是猜测要是根据原库文件把这个找不到的软连接文件创建出来，会是一个什么样的效果呢？？

[root@pxc02 mysql3308]#  ldd /usr/local/mysqlpxc/bin/mysql
linux-vdso.so.1 =>  (0x00007ffc45bdf000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f6e54cf4000)
libreadline.so.7 => not found
libncurses.so.5 => /lib64/libncurses.so.5 (0x00007f6e54acc000)
libtinfo.so.5 => /lib64/libtinfo.so.5 (0x00007f6e548a2000)
libz.so.1 => /lib64/libz.so.1 (0x00007f6e5468c000)
librt.so.1 => /lib64/librt.so.1 (0x00007f6e54483000)
libatomic.so.1 => /lib64/libatomic.so.1 (0x00007f6e5427b000)
libssl.so.1.1 => /lib64/libssl.so.1.1 (0x00007f6e5400d000)
libcrypto.so.1.1 => /lib64/libcrypto.so.1.1 (0x00007f6e53b89000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f6e53985000)
libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f6e53603000)
libm.so.6 => /lib64/libm.so.6 (0x00007f6e53300000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f6e530ea000)
libc.so.6 => /lib64/libc.so.6 (0x00007f6e52d29000)
/lib64/ld-linux-x86-64.so.2 (0x00007f6e554ff000)

于是根据源库文件libreadline.so.6.2 把libreadline.so.7要找的软连接文件创建出来

[root@pxc02 mysql3308]# ln -sv /usr/lib64/libreadline.so.6.2 /usr/lib64/libreadline.so.7
/usr/lib64/libreadline.so.7 -> /usr/lib64/libreadline.so.6.2

[root@pxc02 mysql3308]# ll /usr/lib64/libreadline.so.7
lrwxrwxrwx 1 root root 29 Feb 24 09:46 /usr/lib64/libreadline.so.7 -> /usr/lib64/libreadline.so.6.2
[root@pxc02 mysql3308]# find / -name 'libreadline.so*'
/usr/lib64/libreadline.so.7
/usr/lib64/libreadline.so.6.2
/usr/lib64/libreadline.so
/usr/lib64/libreadline.so.6

检测如下：发现不在报错，问题解决。

[root@pxc02 mysql3308]# ldd /usr/local/mysqlpxc/bin/mysql
linux-vdso.so.1 =>  (0x00007fffbeb64000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f9cef24a000)
libreadline.so.7 => /lib64/libreadline.so.7 (0x00007f9cef004000)
libncurses.so.5 => /lib64/libncurses.so.5 (0x00007f9ceeddc000)
libtinfo.so.5 => /lib64/libtinfo.so.5 (0x00007f9ceebb2000)
libz.so.1 => /lib64/libz.so.1 (0x00007f9cee99c000)
librt.so.1 => /lib64/librt.so.1 (0x00007f9cee793000)
libatomic.so.1 => /lib64/libatomic.so.1 (0x00007f9cee58b000)
libssl.so.1.1 => /lib64/libssl.so.1.1 (0x00007f9cee31d000)
libcrypto.so.1.1 => /lib64/libcrypto.so.1.1 (0x00007f9cede99000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f9cedc95000)
libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f9ced913000)
libm.so.6 => /lib64/libm.so.6 (0x00007f9ced610000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f9ced3fa000)
libc.so.6 => /lib64/libc.so.6 (0x00007f9ced039000)
/lib64/ld-linux-x86-64.so.2 (0x00007f9cefa55000)
[root@pxc02 mysql3308]#  /usr/local/mysqlpxc/bin/mysql -uroot -p',pL*O3dLkW
3476
k)'
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
[root@pxc02 mysql3308]# ldd /usr/local/mysqlpxc/bin/mysql

总结：发现解决此问题简单了不少。遇到问题一定要先看下报错，做下简单的分析，不要盲目的直接google和百度。要有针对性的解决问题。